Jumbo Frames and DF bit

[Walter Dey]

Enabling Jumbo Frames on UCS doesn't seem to set the DF bit ? correct ?

Can this be set by UCSM and/or CLI ?

[richbarb]

Hello Wdey,

Enabling jumbo frames doesn't touch in the df-bit.

To enable JUMBO in the UCS, you can follow this great guide created by Peter Revil.

http://www.ccierants.com/2013/10/ccie-dc-definitive-jumbo-frames.html

There is a specific section to enable jumbo on UCS.

[Walter Dey]

Thanks for this pointer

UCS customer uses Jumbo frames for NFS, connecting to a Netapp Filer which is in a different IP subnet.

He compared performance with standard Ethernet frame size and Jumbo frames, and didn't see any difference.

I therefore proposed to do a test from ESXi

vmkping -I vmk2 -d -s 9000 192.168.......

vmkping -I vmk2 -d -s 1500 192.168.......

which fails, however

vmkping -I vmk2 -s 9000 192.168.......

vmkping -I vmk2 -s 1500 192.168.......

works ok

Therefore, somewhere in the network between UCS and Netapp, there must be a problem.

It seems, that typical OS (e.g. ESXi) don't set the DF flag.

[richbarb · Accepted solution]

Once I did the test about the jumbo frames network performance and can't see any significant difference.

In that time I used a oracle RAC installed in the UCS and a NetApp Filer with DNFS configuration.

In the UCS you must configure MTU in two different places (QoS configuration and vNIC configuration).

In your test with df-bit flag enabled use the packet size maximum of 8972.

[Walter Dey]

8970 was the solution ! Thanks Richard !